Thermoplastic stiffener



Patented May 20, 1941 UNITED STATES' PATENT OFFICE THERMOPLASTIC sm'rnnna Roy S. Ritchie, Newark, N. 1., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Application April 22, 1939,

Serial No. 269,467

4 Claims.

-This invention relates to thermoplastic compositions and to flexible, fibrous sheets impregnated therewith. It relates particularly to such impregnated sheets adapted to be used in making box toes or other shaped articles.

A wide variety of substances have been proleather and the cloth lining of a shoe.

A solvent box toe is made from a fibrous sheet material coated with a liquid cellulose ester composition such as a solution comprising cellulose nitrate or cellulose acetate. In

order touse this type of impregnated material in making box toes, it must be soaked in a solvent to soften the cellulose ester composition with which the blank is impregnated, since the blank will not adhere to leather or cloth if the solvent is not present. Furthermore, the solvent must be uniformly distributed throughout the cellulose ester impregnating material and for this reason solvent box toe blanks must be stored in closed containers in contact with the required solvent. The softened blank, still containing volatile solvent, is forced into shape and adheres to adjoining lining-and upper because of the tacky nature of the solvent-softened surface. A necessary limitation. and disadvantage of the solvent box toe is that all of theshoe manufacturing operations must be. completed before the solvent evaporates. Furthermore, simply dipping such cellulose derivative coated fabrics in a' solvent does not soften them throughout, which is a condition necessary to ,thermoplastic box toe, has heretofore comprised a fibrous base, usually felt or paper, im-

pregnated with black asphalt. The cellulose esters are not sufficiently adhesive at their softening points, or have too high softening points to be employed in thermoplastic box toes without injuring the leather unless solvents are used. a

The black asphalt usually employed in this type of toe-forming materials stains everything with which it comes in contact, especially when heated, and therefore cannot be employed in the manufacture of the better quality lightcolored or white shoes.

Refined rosin and other resinous'or waxy materials have been suggested and tried as the indurative for thermoplastic box toe forms. The recognized shortcoming of these agents alone is increase their plasticity at working temperatures dered adhesive by dipping in solvent priortoy use. .The use of the "solvent or canned box toes is further hamrdous to health of operators because of the toxic nature of solvent vapors and because of the flammability'of the solvents The third class of box toe, known as the that, like asphalt, they have-too low a viscosity when hot, and when cooled they are too brittle, tending to powder and separate from the felt or paper support when'the latter is flexed.

From practical considerations, the thermoplastic material with whichthe fibrous base is impreganated should be capable of being apin shoe machinery but must not have so low a viscosity that it is easily displaced or squeezed from the base during the pull-over and bedlasting operations. must further be as light colored as possible and should not stain leather or fabric.

It is, accordingly, among the objects of the invention to provide a composition of matter suitable as an indurative for flexible fibrous materials used in box toe manufacture, which'is It must soften and be-, come adhesive at temperatures easily attainable The impregnating material capable of being applied as a melt at mr'ideratetemperatures. It-is a further object to provide or fabric, and which will adhere readily there to when softened by heat without the use of solvents. It another object to provide a flexible fibrous sheet material impregnated with a enough to withstand the pull-over operation in making shoe toes, characterized by its strong adherence to leather and cloth'at the working such a composition which'will not stain leather composition as aforesaid, the article being tough ing under temperatures normally met with in 1 shoe wear. It is a particular object to provide a box'toe blank of suitable stifiness and resil ience, comprising a textile. fabric impregnated temperatures available in customary bed-lasting pressure in the pulling-over and bed-lasting operations, Further, the cellulose ether-resin indurative is tough'enough when cold to permit the box toe to be skived readily.

Although canton flannel or like absorptive woven fabric is preferred as a base for impregnation with the new composition to yield a ther moplastic box toe of greatly improved properties,

felt or absorbent paper may be employed as the with the new composition and which will have;

the aforesaid desired characteristics. r

According to the present invention, the foregoing and related objects are attained through the employment as the thermoplastic adhesive in box toe manufacture of a particular type of bomposition comprising a major proportion of a relatively low melting resin and minor proportions of cellulose ethers and plasticizers. The said composition, to be more fully described hereinafter, is employed as a molten composition to impregnate a flexible base which is preferably a woven fabric such as cotton flannel, or it may be a self-supporting felted flexible fibrous sheet such as felt or paper. The flexible supporting base is impregnated by immersionin the heated liquefied thermoplastic and the fabric, or cther fibrous base, is removed from the impregnating bath, doctored, or passed between rollers to provide a uniform Weight of impregnating thermoplastic to a given area of fibrous base, suitably 8-16 ounces per square yard, The impregnated fabric is then cooled away from contact with outside surfaces until the plastic composition has set, and. subsequently cut and shaped into the desired form and size. Box toe blanks cut from the so-impregnatedfibrous sheet can be applied to shoes at. moderate. temperatures, e. g. 180-250 F., without the use of volatile solvents in the customary -pull-over or bed-lasting operations in shoe manufacture to form a"stiff, resilient, non-staining adherent toe stiffener.

Of the fibrous base materials available for use in making box toes, it has long been recognized that a woven fabric such as cotton flannel would be preferable to the felted fibrous materials, such as felt or paper, which are commonly used in this art. Cotton flannel has not been used as a base for impregnation with melted rosin or asphalt because the impregnated flannel could, not 7 be satisfactorily skived. The art was thus left to use a fibrous base having little mechanical strength and an 'impregnant which became so fluid 'at elevated temperatures that it did not improve the tear strength of the fibrous base. This factor is important because the box toe material issubjected to the severest strains when it has the, least mechanical strength, namely in the pullin'g-ove'r and bed-lasting operations when the box toe is soft and adhesive from the applications of heat. v The-preferred combination, of a woven fabric which has high mechanical strength and a resin- .fibrous base. When impregnated with the resintrade, which melt at temperatures below 160 C. I

and preferably those which melt between 115 .and 150 C. The resins employed may be either synthetic or natural, provided that on continued heating at temperatures up to about 150 C. in the presence of a cellulose ether they are not converted into higher melting or infusible products. Among the resins which have been found satisfactory are rosin, dammar, run natural resins, the rosin esters such as ester gum, lower alkyl rosin esters and the like, phenol-modified copals, non-thermosetting phenol-formaldehyde resins, cumarone-indene resins and their phenolmodified products, and the like. The natural resins and their chemically modified derivatives are preferred. a

The cellulose ethers which may be employed in the preparation of the thermoplastic adhesives peratures at or below 150 C., and that it be ous impregnating material which has high viscosity' at elevated temperaturesjby virtue of its cellulo'sfeether' content is a great improvement over the prior art, thermoplastic. toe in which the indurative becomesjso fiul'd under shoe making t prevents the thermoplastic miscible with the resin employed. The cellulose ether may preferably be further characterized by having a relatively low intrinsic viscosity, and there is used especially advantageously an ethyl cellulose, the viscosity of which, in 5 per cent solution in :20 toluenezethanol, is below 30 centipoises. Even small amounts of a low viscosity cellulose ether materially increase the viscosity lose ether may first be plasticized by intimately mixing the same with up to an equal weight of then adding the cellulose ether, stirring for a few minutes until the cellulose ether dissolves, then chilling back toward 150 C. by the addition of cold plasticizer,

tively, of the resin"employed.' The amount of plastlcizer may vary from 3 to 18 parts for each The preferred amount of cellulose ether in the compositions is about u 10 to 30. parts for each to 70' parts, respecthe composition if desired.

Each of the following examples illustrate a composition which has been employed satisfactorily in the preparation of box toes. The com-' position in each instance was prepared by melting the resin in a saturation tank while heating until the temperature was approximately 150 C. To the melted resin was added a plasticized cellulose ether. The mixture was thoroughlystirred until a uniform melt was obtained. A sheet-of cotton flannel, felt, or paper was then passed into and through the solution, being conveyed therethrough in 'a manner such that the sheet became completely impregnated. The impregnated sheet was withdrawn from the bath, passed between heated rollers or heated scraping knives to remove excess composition, and then conveyed with cooling out of contact with other surfaces tion was no longer tacky. It was then cut, shaped, and built into a shoe in the customa manner.

When fibrous materials, such as canton flannel, were impregnated with the above compositions and molded, or otherwise shaped for use as box toes, the formed product was stiff enough to retain its shape under severe service conditions, yet flexible enough to be adapted to use in the better class dressy shoes as well as in service or -wor shoes. The thermoplastic impregnated fabric did not crack or break when parted to the composition of Example 4 a resilience and an adhesive quality unexpectedly bility, the odorless, non-staining, substantially colorless ethyl cellulose compositions of the other examples are to be preferred in rthermoplastic box toes.

Other modes of applying the principle of my I invention may be employed instead of those explained, change being made as regards the materials or method employed, or the article thereby for at least 10 feet until the indurative composi- Example 1 Per cent Wax-free dammar 75 Standard ethoxy, low viscosity, ethyl cellulose 17.5 Castor oil 7.5

Example 2 I Per cent Elemi 73 Ethyl cellulose 18 Diphenyl mono-ortho-xenyl phosphate 9 Example 3 Per cent Rosin 75 Ethyl cellulose 17.5 Dibutyl phthalate 7.5

Example 4 i 1 Per cent Wood rosin 74.6 Benzyl cellulose, medium viscosity 12.7 Dibutyl phthalate 12.7 Example 5' Per cent Wood rosin 76 Ethyl cellulose (standard ethoxy, centipoise) Dibutyl phthalate; 7.5 Titanium oxide 1.5

flexed and the indurative composition showed no tendency to powder or crumble.

The inherent softness of benzyl cellulose improduced, provided the materials, methodor article set forth in the following claims or the equivalent of such stated materials, method or durative consisting essentially of between about 8.5 and 30 per cent of a cellulose ether, between 3 and 18.5 per cent of a softening plasticizer for the cellulose ether and from 60 to 87.5 per cent by weight of a fusible non-setting resin compatible in the molten state with the. cellulose ether, the said resin being selected from the group consisting of the natural resins and their chemically modified resinous derivatives.

2. A thermoplastic sheet suitable for making box toes and the like consisting essentially of an absorbent flexible fibrous base and, as an indurative therefor, a compositionfusible below C. which is viscous and highly adhesive when warm, and tough, non-tacky and substantially nonpowdering at room temperature, the said indurative consisting essentially of between about 8.5 and 30 per cent of a cellulose ether, between 3 and 18.5 per cent 'of a softening plasticlzer for the cellulose ether and from 60 to 87.5 per cent by weight of rosin.

3. A thermoplastic sheet suitable for making box toes and the like consisting essentially of an absorbent flexible fibrous base and, as an indurative therefor, a composition fusible below 150 C. which is viscous and highly adhesive when warm, and tough, non-tacky and substantially non-powdering at room temperature, the said indurative consisting essentially of between about 8.5 and 30 per cent of ethyl cellulose, be-

tween 3 and 18.5 per cent of a softening plasticizer for the ethyl cellulose, and from 60 to 87.5 per cent by weight of a fusible non-settingnatural resin compatible in the molten state with the ethyl cellulose. 1

4. A thermoplastic sheet suitable for making box toes and the like consisting essentially of an absorbent flexible fibrous base and, as an -in, durative therefor, a composition fusible below 150 C. which is viscous and highly adhesive when warm, and tough, non-tacky and substan- 'tially non-powdering at room temperature, the said indurative consisting essentially of between about 8.5 and 30 per cent of ethyl cellulose, between 3 and 18.5 per cent of a softeningplasticizer for the ethyl cellulose, and from 60 to 87.5 per cent by weight of rosin.

ROY S. RITCHIE. 

